Our experiments concern the acquisition by children between the ages of five and twelve of specific structures and rules in stress phonology, syntax, and semantic interpretation. Examples are: 1) how does a child learn the rules that shift stress in "theatre", "theatrical", and "theatricality"? 2) how does a child learn that "all" may refer to either "circles" or "black" in "the circles are all black"? 3) how does a child learn that anyone can be singing in "he hates singing" but "he" must be singing in "he hates singing arias"? Each of these examples involves precisely defineable issues in a child's acquisition of structure-dependent knowledge. Because the issues involve fundamental forms of human cognition, the relevance of our studies in language goes beyond language; we expect our work to contribute to an overall view of a child's mental development. In particular, our work is relevant to Piagetian views of mathematics, problems of aphasia, and the spelling used in readers. Our methods involve creating a game-like atmosphere in which to elicit children's sentences, preferences in grammatical forms, and choices among pictures. Older children will be asked to read nonsense and real words. There will be nothing coercive, corrective, or frustrating for the children. We shall give no rewards. (In our experience with over 500 children in different countries and different social classes, we have found that children enjoy such games.) The larger goals of our research is to construct a model of a mechanical procedure of hypothesis construction that can explain a child's capacity to learn the structure of the language in his environment and use it creatively.